Handedness index

Films of pure CNLCs have a unique transmission behavior as CP light with the same sense of circular polarization as the CNLC is filtered out by reflection, while CP light of the opposite handedness as the CNLC film is transmitted. This selective optical transmission characteristic is referred to as a one-dimensional photonic stop-band or a selective reflection band. The stop-band is centered at a certain wavelength Ac, which is dependent on the pitch length p and the average refractive index n of the CNLC ... 

Fig. 4.11c. Subsequent removal of the molecules using the STM tip reveals that their adsorption resnlts in the removal of Cn atoms from the rows of the Cu(llO) snrface structure and the formation of pits in the snrface. Examination of the perimeters of the pits reveals that they have two kinks and that those kinks impart the same handedness to the pits as the kinks on a high Miller index CwQikl) surface. Once again, the chirality of an adsorbed molecnle has been imprinted into the structure of an otherwise achiral snrface.

Lyotropic liquid crystalline cellulose derivatives exhibit unique optical properties because of their helicoidal supramolecular structure.The chiro-optical properties of the helicoidal structure can be described by a pitch p (or its inverse, the twist p ) p = 2o/fi, where is the reflection wavelength and h is the mean refractive index of a sheet, and the corresponding handedness of the twist right-handed helicoidal structure being assigned to a positive pitch p > 0) and left-handed helicoidal structures to a negative pitch p < The nematic mesophase can be... 

Cell thickness-dependence of the reflection of a cholesteric liquid crystal in the planar state. The pitch of the liquid crystal is P = 350 nm. The refractive indices of the liquid crystal are tig = 1 -7 and = 1.5. The liquid crystal is sandwiched between two glass plates with the refractive index = 1.6. The incident light is circularly polarized with the same helical handedness as the liquid crystal. Neglect the reflection from the glass-air interface. Use two methods to calculate the reflection spectrum of the liquid crystal with the following cell thicknesses P, 2P, 5P and lOP. The first method is the Berreman 4x4 method and the second method is using Equation (2.186). Compare the results from the two methods. 

Both the pitch and handedness of the cholesteric helices can be detected by chiroptical techniques, optical rotatory dispersion (O.R.D.) and circular dichroism (C.D.), by characterizing the selective reflection band. A right-handed helix (P-helix) originates a negative reflection Cotton-effect and vice versa (A = np where is the wavelength of the reflection band, n the main refractive index and p the pitch). 

The behavior of the output beam depends on the amplitude of the PZTs, since this amplitude determines the change in refractive index along the stress axis. At a certain amplitude, the maximum phase retardation for a particular wavenumber (vo) is 90° and the beam emerging from the ZnSe plate becomes circularly polarized. The handedness of the circularly polarized radiation switches sinusoidally from left to right with a frequency equal to the frequency at which the ZnSe plate is being extended and compressed. (It is this property that is used for the measurement of VCD spectra.) For most other wavenumbers in the spectrum, the radiation is elliptically polarized, with the ellipticity increasing with the difference between... 

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